The invention relates to a process for coding digital video data in respect of the compressing of these data and the transmitting of region information relating to the coded video images. It also relates to a device for implementing the process.
Techniques for compressing video data are known as being described, for example, within the MPEG2 standard. However, these techniques do not utilize the data relating to the segmentation of the image, for example region information. The additional information to be transmitted demands a higher cost of transmission for a given image quality or else renders the coding incompatible with the standard.
The purpose of the present invention is to remedy the aforementioned drawbacks.
To this end, the subject of the invention is a process for the compression of digital data from a video image which carries out a partitioning of the image into image blocks, a Discrete Cosine Transformation of these blocks so as to deliver coefficients and a quantization of each coefficient using a quantization interval, characterized in that it also carries out a segmentation of the image and a labelling of the regions obtained, and in that it associates with each block a block control interval on the basis of which the quantization interval for each coefficient of the block is defined, the value of which is calculated as a function of these labels.
The subject of the invention is also a device for the compression of digital data from a video image for the implementation of the preceding process, comprising a circuit for partitioning the image into image blocks, a Discrete Cosine Transformation circuit which carries out such a transformation of the image block into blocks of coefficients, a quantization circuit for quantizing the coefficients belonging to this transformed block on the basis of a control interval, a control circuit which calculates an image control interval as a function of a set-point bit rate for the data output by the device, characterized in that it includes a segmentation circuit which receives the digital data so as to define regions and deliver to the quantization circuit, for each block, a label relating to the region to which it belongs and in that the quantization circuit modifies, before making use thereof, the control interval as a function of this label so as to deliver a block control interval for each image block.
The subject of the invention is also a device for the expansion of video data which receives data compressed according to the above-described process, which video data relate to image blocks belonging to various regions of the image and to control intervals assigned to each block, comprising a circuit for dequantizing the coefficients belonging to an image block, an Inverse Discrete Cosine Transformation circuit which carries out such an inverse transformation of the image block, characterized in that it includes means for determining the region to which the block belongs on the basis of the control interval received in respect of this block.
Thus, the region information is xe2x80x9ccarriedxe2x80x9d by the information relating to the control interval.
By virtue of the invention, the region information can be transmitted almost without degrading the quality of the image, for a given transmission bit rate. The coding process remains compatible with the MPEG standard when the latter is adopted.
Other features and advantages of the invention will emerge clearly from the following description given by way of non-limiting example and offered in conjunction with the appended FIG. 1 which represents a device according to the invention.
The device described in FIG. 1 is explained below.